Treatment of metals



1933- H. N. GILBERT TREATMENT OF METALS Filed Oct. 10 1930 2Sheets-Sheet 1 FIG.1

F i VENTOR BY ATTORNEY Oct. 17, 1933. H. N. GILBERT 1,931,144

TREATMENT OF METALS Filed Oct. 10 1930 2 Sheets-Sheet 2 l 2 24" I j 4 4ATTORNEY Patented Oct. 17, 1933 UNITED STATES" PATENT OFFICE slgnor, bymesne assignments, to E. I. du Pont de Nemours and Company, acorporation of Delaware Application October 10,

5 Claims.

This invention relates to the treatment of molten metals and moreparticularly to the introduction of a metal into the molten bath ofanother.

Certain light metals such as aluminum are commonly used to treat othermolten metals, for instance, molten steel. The result of such treatmentis the removal of objectionable elements, such as sulfur, oxygen, etc.It has been proposed to use certain reactive metals, for instance thealkali metals for this purpose. However, use of these metals has notbeen found practical because of the great difference between theirboiling points and the temperature of the molten metal being treated.This difference in temperature causes sudden vaporization when thereactive metal is added to the metal being treated, which results inmuch of the reactive metal being thrown out of the treating vessel asvapor before it has an opportunity to react with the undesirableconstituents of the metal being treated. Furthermore, this suddenvaporization often causes dangerous explosions.

In the preparation of alloys, the common practice is to add solid metalto the molten bath of another, or to mix the molten metals. Suchprocesses have not been heretofore easily and economically carried outwithout exposure of the molten metals to the atmosphere, with resultantloss by oxidation. Such loss is especially significant when working withreactive metals, for instance, alkali metals. These procedures alsoinvolve danger to workmen, for instance by explosions caused by rapidoxidation of analkali metal or poisoning caused by the fumes from openpots of metals such as lead or mercury. Furthermore, oxidation of themetals usually result in a certain amount of oxide inclusion in theproduct.

One object of my invention is to provide a method and means forintroducing a metal having a low boiling point into a bath of moltenmetal whereby danger of explosions and loss of the low-boiling metal areeliminated. Another object is to provide method and means of introducinga metal or alloy into a molten bath of other metal or alloy whereby lossof metal and other disadvantages caused by oxidation are eliminated.

Other objects will be hereinafter apparent.

These objects are accomplished according to my invention by introducingmetal vapor into a body of molten metal.

Figures 1 and 2 show forms of apparatus suitable for practicing myinvention. In Figure 1, 8

1930. Serial No. 487,778

is a cylindrical steel tank, mounted in a furnace 13, made of refractorymaterial. A cover 4 is screwed on the tank 3 and is fitted with mealinlet tube 1, gas inlet tube 5 and vapor exit tube 6. Tube 1 is fittedwith a closure cap 2 at the upper end. The tube 6 is covered at itsextremity by a refractory coating 10. Tube 5 is connected by means ofthe T-joint 1'? to gas supply line 12. A safety release valve 9 isconnected to line 12. One arm of the T-joint 17 is connected to the sideof the metal inlet tube 1 by means of the tube 16. 7 and 8 are valves intubes 5 and 16 respectively. 15 is a gas burner fitted with gas and airinlet lines 21 and 22 and their respective control valves 23 and 24. 14is a rocker element of which there are two. 19 is a container for moltenmetal, having a refractory lining 11.

In Figure 2, like reference numbers refer to similar elements. Gas inlettube 16 is connected to the tank 3 through the side wall outside thefurnace 13. 20 is a union connection in gas inlet tube 5'. Tube 6' isconnected to the tank 3' through the side wall of tank 3. 18 is acircular cover fastened to tank 3 by means of bolts 25 am. the flange26.

One method of carrying out my invention may be described by reference toFigure 1. A quantity of low-boiling metal, for instance an alkali metal,is charged into the tank 3 through tube 1, which i. then closed with cap2. The tank is heated by means of the burner 15 until the alkali metalreaches a temperature of about 30130 C. below its boiling point. Theapparatus is then ready for use.

A crucible 19, containing molten metal to be treated, is placed beneaththe end of the vapor exit tube 6. Valve 7 is then closed and valve 8opened, thus forcing nitrogen through the system. The apparatus is thentilted on the rockers 1'. until the tube 6 dips to a sufficient distancebelow the surface of the molten metal bath. The steam of nitrogenflowing through the system prevents metal in the crucible from enteringand solidifying in tube 6. Valve 7 is then opened and valve 8 is closed,thus forcing the nitrogen stream through the molten alkali metal in tank3. Due to the high vapor pressure of the metal at the temperatureemployed, alkali metal vapors are swept out through tube 6 with thestream of nitrogen and into the metal in crucible 19. As the metalvapors are introduced into the molten metal being treated they are firstsubstantially completely absorbed. In a short time, depending upon theamount of metal being treated and its composition, vapors of alkalimetal appear at the surface of the metal bath, indicating that thetreatment is nearing completion. Valve 8 is then opened and valve 7closed thus causing almost pure nitrogen in place of metal vapor to flowthrough tube 6, and the apparatus is tilted back to remove tube 6 fromthe molten metal bath.

It the apparatus shown in Figure 2 is used the procedure issubstantially identical with that given above, except for a diflerencein the manner of charging tank 3'. This is done by disconnecting gasinlet tube 5' at the union joint 20, and removing the bolts that securecover 18 to Cover 18, with the section of tube 5' fitted to it, is thenremoved and alkali metal is charged into the tank 3'. Cover 18 is thenreplaced, and line 5 is reconnected by union joint 20. The subsequentprocedure is the same as when using the apparatus shown in Figure 1.

Example Sixty pounds of molten cast iron was treated with sodium by themethod above described, using the apparatus shown in Figure 2. Beforepassing nitrogen through the sodium the latter was heated to atemperature of about 750-800 C., and

this temperature was maintained during the treating operation. Thesodium vapors, when first introduced into the molten cast iron werecompletely absorbed. After a period of two minutes, vapors were observedat the surface of the cast iron. At this moment a sample of the bath wastaken. Analyses of the original iron and this sample showed the sulfurcontent to have been materially decreased.

' While I prefer to heat the low-boiling metal used as treating agent toa temperature of -130 C. below its boiling point, other temperaturesabove and below this range may be used without departing from the spiritand scope of my invention. At temperatures below this range, the amountof metal vapor produced by a given rate of flow of nitrogen to theapparatus will be correspondingly less. At temperatures close tothe'boiling point of the metal relatively large amounts of vapor areproduced by a given nitrogen flow. 11' the temperature is raised abovethe boiling point of the light metal the nitrogen flow may be greatlyreduced or even dispensed with altogether. This method however, has thedisadvantage that when treating batches of metal fumes of low-boilingmetal vapor are introduced into the atmosphere while the end of tube 6is being removed from one crucible into another.

One method of operating with a minimum nitrogen flow comprises startingthe operation at a temperature below the boiling point, as describedabove. As soon as possible, after the tube 6 has been dipped into themolten metal bath, the temperature is raised above the boiling point ofthe light metal and the nitrogen flow either greatly reduced or shut offentirely.

My invention is applicable to the treatment of molten metals with anymetal or alloy which possesses an appreciable vapor pressure at thetemperature at which it is desired to operate.

The temperature of the molten metal into which the metal vapors areintroduced may be either above or below the temperature of the vaporsintroduced. Thus, by my processysodium vapors at 600 C. may beintroduced either into molten lead at 400 C. or molten steel at 1500 C.

Besides nitrogen, other gases which do not react to a material extentwith the metals, for instance hydrogen, may be used.

My invention may be used to prepare alloys, where exclusion of air fromone or both the metals alloyed is desirable. For instance, by addingsodium vapor to a body of molten lead to make sodium-lead alloy, theformation of sodium oxide is reduced, and the hazard of handling hotsodium in the open air is avoided. If it is also desired to protect thealloy from oxidation, the vessel holding the molten metal may be madepart of a closed system, through which nitrogen or other inert gas iscirculated to remove all oxygen before the metal is melted.

Other variations of and uses for my invention will be apparent to thoseskilled in handling metals.

The specific forms of apparatus shown in the drawings are given only byway of illustration and other forms are possible without departing fromthe spirit and scope of my invention. The essential elements in myapparatus are a container for molten metal with means of heating thesame, a means for introducing gas below the surface of molten metal insaid container, means for conducting vapor-from the container and meansfor introducing the vapor below the surface of a second body of moltenmetal.

I claim:

l. A process comprising passing a substantially inert gas through a bodyof molten metal to produce a mixture of said gas and vapor of said metaland passing said mixture into a body of other molten metal.

2. A process comprising passing a substantially inert gas through a bodyof molten alkali through a body of molten sodium maintained at 750-850"C. to produce a mixture of nitrogen and sodium vapor and passing saidmixture into a body of other molten metal.

5. A process comprising passing nitrogen through a body oi. moltensodium maintained at ISO-850 C. to produce a mixture of nitrogen andsodium vapor and passing said mixture into a body of molten steel.

HARVEY NICHOLAS GILBERT.

